Most artificial satellites, spacecraft and other craft, such as aircraft, ships and ground vehicles (collectively referred to herein as vehicles), require information about their locations and/or attitudes to accomplish their missions. This information may be obtained from one or more sources, such as ground-based radar tracking stations or on-board global positioning system (GPS) receivers, inertial guidance systems (INS) and/or star trackers.
A star tracker is an optical device that measures angles to one or more stars or other sufficiently bright celestial objects with known ephemerides, as viewed from a vehicle. A star tracker typically includes a catalog that lists bright navigational objects and information about their locations in the sky, sufficient to calculate a location of a vehicle in space, given bearings to one or more of the objects. A conventional star tracker includes a lens that projects an image of a celestial object onto a photocell, or that projects an image of one or more celestial objects onto a pixelated light-sensitive sensor array. The lens typically constitutes a large fraction of the volume and the mass of a star tracker. An ideal star tracker would be mechanically and optically simple, small and low in mass.